Progress in mobile communications is not limited to consumer usage fields using voice or data transmission, represented by smartphones and tablets, but extends to a telemetry field that has been constructed as a dedicated system. Recently, usage of M2M (Machine to Machine) using an inexpensive and small-size wireless module is progressing. Unlike consumer usage traffic, periodical traffic with a small amount of information occurs in M2M.
A wireless module for M2M (hereinafter also referred to simply as a wireless module) is configured with a wireless transceiver and an external antenna. For example, a wireless transceiver designed to properly operate in a 2 GHz band and an 800 MHz band and an externally installed loop antenna having both of the 2 GHz band and the 800 MHz band as operating frequency bands are known. The wireless transceiver is, for example, built into a handy terminal or a vending machine. The external antenna is connected to an antenna terminal of the wireless transceiver and is installed, for example, as an antenna of a handy terminal or on the top of a vending machine. In general, in the wireless module, it is not necessary to integrally install the wireless transceiver and the external antenna. Thus, unlike smartphones, tablets or mobile phones for consumers, the wireless module has an implementation form with a high degree of freedom.
As the external antenna, various products are provided (for example, see Non patent document 1). The above loop antenna having both of the 2 GHz band and the 800 MHz band as operating frequencies has the following specifications: outer diameter: 150 mm×40 mm×60 mm; 2 GHz band gain: −8 dBd or more; 800 MHz band gain: −7 dBd or more; and weight: 220 g. Further, such an antenna is also known that a printed-circuit board on which an antenna pattern is printed is built into a plastic housing, and its electrical characteristics are almost similar to those of a loop antenna.
As an example of a conventional wireless module for M2M, an example of operating in both of the 2 GHz band and the 800 MHz band as described above is known. Due to increase in the number of frequency bands for mobile phones, it is thought that the number of frequency bands that can be used in a wireless module also increases. From the viewpoint of characteristics of a wireless module, frequency bands used for wireless communication are not necessarily required to be frequency bands for mobile phones, and furthermore use of various frequency bands, such as frequency bands used by specified low-power equipment, frequency bands for RFID and the like and frequencies bands for wireless LAN, is conceivable though there are preconditions to meet certain technical standards.